1. Field of the Invention
The present invention relates to an insertion device for a deformable intraocular lens that is inserted into the eye in place of the natural lens when the latter is physically extracted because of cataracts.
2. Description of the Related Art
Conventionally, many types of such intraocular-lens insertion devices have been proposed.
When an intraocular lens having coil-shaped supports is inserted into the eye by use of an intraocular-lens insertion device, the intraocular lens may be abruptly ejected from an open end of an insertion end portion of the insertion device due to elastic restoration force of the intraocular lens. In order to mitigate the problem of such abrupt ejection, the assignee of the present invention has proposed an improved insertion device capable of controlling the final insertion speed at which an intraocular lens is inserted in the eye (Japanese Patent Application Laid-Open (kokai) No. 08-038542).
That is, in the insertion device disclosed in Japanese Patent Application Laid-Open No. 08-038542, a slit is formed in the insertion end portion made of elastically deformable plastic. Immediately before a folded intraocular lens is ejected from the open end of the insertion end portion of the insertion device and is allowed to restore its predetermined original shape, the slit allows a portion of the intraocular lens to project outside therethrough in order to partially absorb elastic restoration force. In addition, cut surfaces located above and below the slit come into contact with portions of opposite faces of the intraocular lens and nip the intraocular lens, to thereby prevent abrupt ejection of the intraocular lens from the open end of the insertion end portion by means of frictional force.
Such a convention insertion device for a deformable intraocular lens will be described with reference to FIGS. 13 to 17. FIG. 13 is a partially cutaway perspective view of a conventional insertion device for a deformable intraocular-lens. FIG. 14 is an enlarged perspective view of the insertion end portion of the insertion device. FIG. 15 is a cross sectional view taken along line XV—XV of FIG. 14. FIG. 16 is an enlarged perspective view of the insertion end portion of the insertion device which is used for description of operation. FIG. 17 is a cross sectional view taken along line XVII—XVII of FIG. 16.
In FIG. 13, reference numeral 11 denotes a device body; 12 denotes a push rod; 13 denotes a male-thread shaft; and 14 denotes a push-out mechanism.
Reference numeral 18 denotes an enclosing member. The enclosing member 18 is provided with a lens receiving section 16 having a hinge portion 15. An insertion tube 17 projects from the front end of the lens receiving section 16. A tapered insertion end portion 17a of the insertion tube 17 has an axially extending slit 17b. The slit 17b has a length shorter than a portion of the tapered insertion end portion 17a which is to be inserted into the eye through an incision formed thereon.
The slit 17b has a constant width slightly smaller than the thickness of an optical portion 2 of an intraocular lens. For example, when the optical portion 2 has a thickness of 1 mm, the width of the slit 17b is set to 0.9 mm. Reference numeral 17c denotes a base end portion of the insertion tube 17, and 17d denotes an open end.
The conventional insertion device having the above-described structure is used as follows. The intraocular lens 1 is placed on the lens receiving section 16 of the enclosing member 18 and is folded into a smaller size before being loaded onto the insertion device body.
Upon completion of loading of the intraocular lens 1, the male-thread shaft 13 of the intraocular-lens insertion device is rotated in order to screw-feed the push rod 12. As a result, a process of inserting the intraocular lens into the eye starts. Behavior of the insertion end portion 17a of the insertion tube 17 during the above described insertion of the intraocular lens into the eye will be described with reference to FIGS. 16 and 17.
The intraocular lens 1 is gradually pushed forward by the tip end of the push rod 12. When the intraocular lens 1 reaches the tapered insertion end portion 17a of the insertion tube 17, as shown in FIG. 17, the axially extending slit 17b of the insertion end portion 17a opens gradually. As a result, stresses in the optical portion 2 of the intraocular lens 1, which has been folded at the base end portion 17c of the insertion tube 17, are gradually released at the insertion end portion 17a. Subsequently, the intraocular lens 1 is inserted into the eye from the open end 17d. 
As shown in FIG. 17, the slit 17b holds the optical portion 2 of the intraocular lens 1 while sandwiching it, to thereby prevent abrupt ejection of the intraocular lens 1 into the eye. In addition, although the slit 17b releases stresses from the intraocular lens 1, the intraocular lens 1 is retained at the insertion end portion 17a, because cut surfaces located above and below the slit 17b hold the intraocular lens 1 from both sides thereof. Moreover, the slit 17b can control insertion speed of the intraocular lens 1 to match advancement speed of the push rod 12.
Moreover, there has been known an insertion device in which a slit and a hole are formed in the insertion end portion, as shown in FIGS. 18 to 20. A slit 17b is formed in the insertion end portion 17a in such a manner that no clearance is formed between upper and lower cut surfaces 17e of the slit 17b; i.e., the upper and lower cut surfaces 17e can come into contact with each other. Further, a hole 17g for crack prevention is formed in the insertion end portion 17a such that the hole 17g penetrates the wall of the insertion end portion 17a perpendicular to the axis thereof and provides an open portion 17k at a base-end-side end portion 17j of the slit 17b. 
However, in the conventional intraocular-lens insertion device, the slit 17b formed in the tapered insertion end portion 17a of the insertion tube 17 has angular corners 17f which are formed between the upper and lower cut surfaces 17e and the inner and outer wall surfaces 17i of the insertion tube 17 and which extend along the axial direction. When the intraocular lens 1 is held within the slit 17b, the angular corners 17f are in contact with the opposite faces of the optical portion 2 of the intraocular lens 1 while biting thereinto. When the intraocular lens 1 is pushed out in this state, large frictional force is generated between their contact surfaces, thereby preventing smooth performance of the push-out operation.
Further, the slit 17b formed in the tapered insertion end portion 17a involves variation in terms of the shapes of angular inner and outer corner portions 17f and the cut surfaces 17e of the slit 17b stemming from errors arising during formation of the slit 17b, whereby pressing force acting on the contact surface of the optical portion 2 of the intraocular lens 1 changes at locations along the slit 17b, resulting in variation in nipping force produced by the slit 17b. 
Moreover, due to the variation in nipping force produced by the slit 17b, anomalous friction force is generated between the cut surfaces 17e and the opposite faces of the optical portion 2 of the intraocular lens 1, whereby the operator experiences difficulty in maintaining stable lens insertion speed and controlling insertion speed with high reproducibility. Therefore, the insertion operation requires skill.
Furthermore, in the conventional insertion device in which the crack prevention hole 17g is formed at the end portion 17j of the slit 17b, as shown in FIG. 20, angular corner portions 17l are formed between the wall of the hole 17g and the cut surfaces 17e at the end portion 17j of the slit 17b. Therefore, the corner portions 17l apply large pressing force to a rear portion of the intraocular lens 1 in the directions of arrow F, so that a difference in nipping force is produced at the end portion 17j of the slit 17b, thereby preventing smooth control of the insertion speed of the intraocular lens.